<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>姓名案例_watch实现</title>
    <script type="text/javascript" src="../js/vue.js"></script>
</head>
<body>
    <div id="root">
        姓：<input type="text" v-model="firstName"><br><br>
        名：<input type="text" v-model="lastName"><br><br>
        全名：<span>{{fullName}}</span>
    </div>
</body>
<script type="text/javascript">
    Vue.config.productionTip=false;
    const vm=new Vue({
        el:'#root',
        data:{
            firstName:'小',
            lastName:'慧',
            fullName:'小_慧'
        },
       watch:{
           firstName(val){
               setTimeout(() => {
                this.fullName=val+'_'+this.lastName
               }, 1000);
           },
           lastName(val){
               this.fullName=this.firstName+'_'+val
           }
       }
    })
</script>
</html>